Field of the Invention
The invention relates generally to monitoring downhole equipment, and more specifically to systems and methods for monitoring temperature and/or temperature distribution in downhole equipment such as electric submersible pump (ESP) systems using magnetostrictive probes.
Related Art
Oil production often requires the use of artificial lift systems to recover oil and other well fluids from wells. These artificial lift systems may include, for example, ESP systems and subsea boosting systems. These systems are typically very expensive to install and operate. A lift system may, for example, cost tens of millions of dollars to install and hundreds of thousands of dollars each day to operate. The costs associated with failures and downtime in these systems are also very high.
Because of the high cost of artificial lift systems, it is very important to take steps to ensure that they are as reliable as possible and have the longest possible operational life. One of the things that can be done to improve reliability in these systems is to monitor various parameters associated with the systems in order to determine their “health”. These parameters may include such things as temperature, pressure, vibration, fluid flow, fluid viscosity, voltage, current, and many others.
If the monitored parameters remain within desired operating ranges (a “green” zone), the system may continue to operate without any changes. If the monitored parameters fall outside the desired operating ranges, but are still within acceptable limits (a “yellow” zone), it may be necessary to adjust the operation of the system in some manner. This may include modifying control signals, updating operating parameters within the downhole equipment, and so on. These adjustments are intended to move the operation of the system (as indicated by the monitored parameters) back into the green operating zone. If the adjustments do not cause the parameters to return to the desired operating ranges, this may indicate that it is necessary to perform repair or maintenance on the system. If the monitored parameters fall outside the range of acceptable values (a “red” zone), it may be necessary to discontinue operation of the system, and possibly repair or replace one or more system components.
One of the key parameters that may be monitored is the temperature of the system components that are positioned downhole within a well. In some applications, the temperature can be as high as 700° F. High temperatures can be very hard on components such as motor bearings, and even materials such as electrical insulation, which may begin to break down and lose its electrically insulating properties. Conventionally, thermal sensors such as thermocouples were designed into equipment such as ESP motors to provide information on the temperature of the equipment. A thermocouple, however, can only monitor the temperature at a single point. For ESP applications, thermocouples can typically only monitor the temperatures near the ends of the motor because these are the only areas that are accessible. A large portion of the motor, especially near its center, is not accessible and consequently cannot be monitored.
It would therefore be desirable to provide means to replace the expensive fiber optics sensors in downhole equipment such as multi-section ESP motors which reduce or overcome one or more of the problems above.